The invention relates to wastewater treatment systems and in particular to wastewater treatment systems in which conversion of organic wastes and light energy to glucose takes place. Specifically, the invention relates to a complex system in which the wastewater and other associated discharges are treated anaerobically and aerobically in a tank complex where waste organics are reduced to inorganic forms available for algal culture in the uniquely designed rapid growth tanks.
Nitrate-nitrogen excessive to the aforementioned growth is removed by aerobic nitrification, anaerobic-denitrification filtration and aeration. Surplus phosphorus is taken out by precipitation and disposal. If algae farming is the objective, these excess nutrients will not be removed, but will also nourish the algae in an enlarged algal growth system. Hydrogen-sulfide gas and sulfides are reduced by anaerobic-aerobic treatment to sulfates to support algal growth. Odors are contained or eliminated in the closed system.
A need has existed for a long time for a system to treat organic wastewaters such as municipal sewage and effluents from food processing plants that economically could support its own operation. This invention provides such a system.
In conventional wastewater treatment systems certain standard or routine processes are utilized. Such conventional systems might include one or several of the following: screening to remove large objects and grit; degritting to remove sand, small stones, and coarse soil particles; comminuting to reduce particle sizes; skimming to remove floating solids, oils, fats, greases, and fuels; sedimentation to remove about 35 percent of the biochemical oxygen demand reduction and 50 percent of the suspended solids in the form of sludge; and flow equalization to store surges and feed them evenly to the process.
The aforementioned conventional processes are usually in a preliminary treatment given to wastewater and is usually determined by the individual characteristics of the wastewater. The various steps aforementioned are selected, sized and sequenced on an "as needed" basis and also as determined for the modes of treatment for further processing. In most conventional systems the subsequent treatment is primarily a treatment to prepare the liquid matter for release into a natural waterway.
In the present invention, the controlled natural purification system provides advanced wastewater treatment, protein conversion, and a recovery system of products for commercial use. As noted hereinbefore, settled wastewater is treated anaerobically and aerobically in a tank complex in preparation for algal growth. Also, as noted hereinbefore, the system of the present invention provides for removal of excessive nitrate-nitrogen and surplus phosphorus, reduction of hydrogen-sulfide gas and sulfides, and the containment or elimination of odors.
The process of the controlled natural purification (CNP) system provides rapid, cost-effective treatment of municipal or food plant wastewater by optimalizing the natural purification process: bacterial oxidation of organic wastes to produce stabilized nutrients (Step 1), for photosynthesis by microalgae (Step 2), and harvesting the algae by a 95% recovery process (Step 3). The resulting products are reusable water and a sterile, stable high-protein algal meal for poultry, swine, or cattle feed.
The invention provides new and novel combinations of sub-processes in reactor vessels and conduits. The Controlled Natural Purification System converts common municipal waste water and food processing plant effluent to reclaimable water and dried algae for use as animal feed. The sale of the algae for animal feed provides the economical advantage of the present invention to pay the cost of the construction and operation of the system. The system provides clean water, converts solar energy to a valuable product, and conserves energy in wastewater treatment. The invented system is such that it can be added to a conventional system as an extension of the prior art.
In natural purification, energy-yielding life processes as bacterial oxidation combine oxygen with organic wastes producing carbon dioxide, water, and energy.
In photosynthesis carried out by algae, energy is fixed as organic matter and oxygen is liberated.
In natural purification, the elements contained in organic matter are repeatedly oxidized and synthesized, gaining energy through the combination of light energy as they pass up the food chain until death and recycle. If the goal of natural purification is recycle, the goal of the Controlled Natural Purification process is controlled recycle. The products of algae meal and reclaimable water become available for recycle at their highest commercial use.
The settled wastewater in the Controlled Natural Purification process is treated for 16 to 24 days in the tank complex (shown in this invention as the B-tank complex) where the waste organics are reduced in carbonaceous and nitrogenous stages to inorganic nutrient forms available for algal growth. Solids in the B-tank anaerobic filters are treated until decomposed.
Bacterial oxidation of organic wastes is completed in sun-lighted tanks (shown in this invention as the A-tank complex) in an O.sub.2 -CO.sub.2 bacterial exchange with algae. The algae photosynthetically metabolize the bacteria-converted nutrients in the CO.sub.2 -enriched culture liquid during two to twelve days retention. The supplemental CO.sub.2, diffused throughout the biomass is a 5% mixture in air, is mostly a by-product of B-Tank aerobic decomposition, and of combustion of hydrocarbon fuels used in algae drying, including process-produced methane. Additional commercially supplied CO.sub.2 is furnished as required.
A biologically-effective light is the limiting factor in the A-tanks, all other variables are aligned to produce maximum algal yield and high effluent quality. After removal of the algae the effluent meets advanced treatment standards. In this final stage, 95% of the algae are separated, concentrated, dewatered, and dried for market.
The removal of sludge and its treatment from raw effluent is a more or less common procedure and is not a part of this invention. This invention deals with the settled wastewater of municipal sewage and organic industrial wastewater such as food plant effluent.
The efficiency of conversion of solar energy to photosynthate has a conservatively projected efficiency in the Controlled Natural Purification reactor of the system of 3.5 percent of bioeffective sunlight, or 1.4 percent of total solar insolation. This conservatively projected efficiency for a parallel at Washington, D.C. and vicinity will produce on a yearly average 9.25 grams per square meter per day of ash-free dry algae, or between 16 and 17 tons per acre per year of dry algae (15 percent ash content). Annual yields will vary at other locations, with available amounts of bioeffective solar radiation.
While this invention proposes the growth of algae for animal feeds (poultry, swine, and cattle), the use of algae for aquaculture, for pharmaceuticals, extraction of pigments (such as chlorophyll and xanthophyll) and for bioconversion to fuels by the use of the system (as well as other technical, medicinal, nutritional, and industrial uses) all are within the scope and intent of this invention.
Algae, in addition to containing 40 to 70 percent protein, is relatively high in xanthophyll. Xanthophyll is a pigment used in poultry diets to impart the desirable yellow color to the skin of the boiler and the egg yolk of the laying hen (dark yellow egg yolks are in demand by the noodle industry). The pigment at present must be derived from natural resources such as corn gluten meal, or marigold meal imported from Mexico and Equador. As to the protein content, algae meal compares favorably with soy bean meal.
Algae as a fuel compares favorably with medium-grade coal: one pound of algae has a heating equivalent of 10,000 BTU's while one pound of medium-grade coal is 12,000 BTU's (or by comparison, the heating capacity of six tons of algae equals that of five tons of medium-grade coal).
Algae can be fermented to produce marsh gas which is 78% methane gas, a fuel with a heating equivalent of 995 BTU's per cubic foot (natural gas is 95 percent methane). One ton of algae will produce about 18,000 cubic feet of methane to produce 2000 to 4000 Kwh of steam-generated electric power, or fermentation of algae can be arrested at the acid-forming stage, producing organic acids which can be processed to alcohol.
The aforementioned food and fuel possibilities of the present invention are presented to point out the economics and energy conservation aspects of the Controlled Natural Purification system of this invention.
Regarding aquaculture, the possibility of algae production through this invention provides the potential for development of an aquaculture industry for fish farming and other related food means (such as tilapia, as fast-growing herbivorous [algae-eating] fish).
Controlled Natural Purification system treatable wastewater is a continuously replenishable resource which, when exploited, diminishes the triple threat to civilization of pollution, shortage of food, and shortage of water. In a like manner, it provides even more tangible benefits to the public in the threats of energy shortage and high food costs. An additional benefit can be tax reduction by reason of the selfsupporting operation of the Controlled Natural Purification system, as well as amortizing the original construction cost.
Food processing companies would also benefit from the recycling investment tax credit (currently 10%, in addition to 10% investment tax credit). When operated for extensive algae farming on organic wastewater of one-third the U.S. population and the food processing plants, the Controlled Natural Purification system could annually produce an estimated ten million tons of high-protein algae on less than one-tenth the acreage now required for soy bean production.
As aforementioned, certain preliminary treatments to the wastewater removes certain ingredients in sludge form so that settled wastewater becomes available for processing in the Controlled Natural Purification system. The removal of these ingredients reduces sludge build-up in the reactor of the system which would require frequent sludge wasting and cleanout of anaerobic filters. Such sludge removal is usually by sedimentation or air flotation.
As noted hereinbefore, the sludge receives separate treatment and is not a part of this invention. That part of any municipal sewage sludge that remains in the Controlled Natural Purification integrated system is processed and disposed by means such as high-rate anaerobic digestion, drying, and landfill. The by-products of the high-rate digesters, methane and carbon dioxide, support the Controlled Natural Purification process (combustion of methane gas provides heat for digesters and partial heat for algae drying).
Any waste heat available, from any source, can be used to heat the settled influent by means of heat exchangers in equalization tanks (shown as E-tanks in the Controlled Natural Purification system), in order to improve the efficiency of the Controlled Natural Purification anaerobic filters.
It is, therefore, an object of the invention to provide a Controlled Natural Purification system to remove from wastewater, by conversion to their nutrient chemical forms, organic wastes that exert biochemical oxygen demand.
It is another object of the invention to provide a Controlled Natural Purification system to maintain a nutrient balance with the optimum light-energy conversion factor.
It is also an object of the invention to provide a Controlled Natural Purification system to use light efficiently so that as many cells as possible are exposed to light and dark for optimal time, at optimal temperature, at economically acceptable cost.
It is also still another object of the invention to utilize supplemental pulsed lighting to significantly increase algae growth by satisfying the algae desire for the light between midnight and the pre-dawn hours.
It is still another object of the invention to provide a Controlled Natural Purification system to deliver, after algae removal, cost-effective, reclaimable water that meets advanced treatment standards.
It is yet another object of the invention to provide a Controlled Natural Purification system to harvest 95 percent of the algae generated.
It is also another object of the invention to provide a Controlled Natural Purification system to dry the algae in a manner to produce a stable, high-quality, commercially-valuable product.
It is yet still another object of the invention to provide a Controlled Natural Purification system to achieve maximum energy savings compared to conventional treatment systems.
It is also still another object of the invention to provide a Controlled Natural Purification system to achieve maximum financial savings compared to conventional treatment systems.
Further objects and advantages of the invention will become more apparent in the light of the following description of the preferred embodiments.